How does amalgam have the same coefficient of expansion as a tooth and why is this useful in dentistry?

Dental amalgam is a mixture of metals, primarily mercury, silver, tin, and copper, used to fill cavities in decayed teeth. One of the key properties of amalgam that makes it useful in dentistry is its coefficient of thermal expansion, which is very similar to that of a natural tooth. This means that when amalgam is used to fill a cavity, it will expand and contract at the same rate as the tooth, reducing the risk of the filling becoming loose or falling out due to temperature changes.

The coefficient of thermal expansion of a material is a measure of how much it expands or contracts when its temperature changes. It is expressed in units of micrometres per metre per degree Celsius (°C). The coefficient of thermal expansion of dental amalgam is approximately 24 µm/m/°C, while the coefficient of thermal expansion of a human tooth is between 11 and 13 µm/m/°C.

By matching the coefficient of thermal expansion of amalgam to that of a tooth, dentists can ensure that the filling will not expand or contract significantly more than the tooth itself, which could lead to problems such as microleakage, cracking, or displacement of the filling. Microleakage occurs when bacteria and fluids can seep between the filling and the tooth, potentially leading to further decay and sensitivity.

The similar coefficients of thermal expansion between amalgam and teeth help to ensure a strong and durable bond between the filling and the tooth, reducing the risk of failure and the need for repeated dental procedures.